Fastener having recess useable with multiple drivers and method of manufacture

ABSTRACT

A fastener is described having a head formed with a recess which accommodates a square head driver, symmetrical drivers, such as PHILLIPS™ style drivers, asymmetrical style cross head drivers, such as POZIDRIV® style drivers, and combination square and cross drivers without compromising performance of the drivers.

CROSS REFERENCE TO A RELATED APPLICATION

This application is a divisional of and claims priority from U.S. patentapplication No. 10/153,547, filed May 21, 2002 which claims the benefitof provisional application Ser. No. 60/360,270, filed Feb. 26, 2002.

BACKGROUND OF THE INVENTION

There are several drivers with specialized engagement surfaces inprevalent use for industrial and domestic purposes. These drivers are,in general, only useable with screws having recesses which match thedrivers. The manufacturing processes for these screws insure a properfit with efficient transmission of torque from the driver to the screws.A common example of such drivers is the Philips head screw driver withits familiar cross wing configuration. A fastener of this type isdisclosed in U.S. Pat. No. 2,046,839 and the disclosure of this patentis incorporated herein by reference. Fasteners of this type are inwidespread use.

Although PHILLIPS head screw are used with great success, a commoncomplaint with regard to such fasteners is that the driver tends to slipout of the recess, when the application of high torque is required. Thisso-called “cam out” occurs because the driving surfaces of the PHILLIPShead fastener taper at an included angle of 8°-27°. In order to overcomethis inconvenience and to provide a fastener which provides a hightorque capability, the driving surface was constructed more vertical asdescribed in U.S. Pat. No. 2,474,994. The disclosure of the '994 patentis also incorporated herein by reference. Fasteners of this type areavailable from licensees of Phillips Screw Company and sold under thetrademark POZIDRIV.

Another type of driver referred to as the “square drive” is designed tofit the Robertson square drive recess and is also in common use.

It is a purpose of this invention to provide a recess which effectivelyaccommodates any of the above drivers and to provide an optimum driveradapted especially for use with this unique recess.

To better understand the invention of this application, it is beneficialto consider the basic process of manufacturing the drivers and matingfastener heads of the above referenced fasteners. It is key in theprocess to construct, to close tolerances, a die which is used to coldform drivers and punches by pressing. Punches are tools used to coldform the recess in the fastener head. Since each element is usedprogressively to obtain the final product, it should be realized thaterrors become compounded throughout the process.

A master tool having all of the attributes of the punch and driver isconstructed as a first step. This tool is generally machined from anappropriate metal blank using an abrasive wheel. In the case of thePHILLIPS cross head tool, this requires four passes, between which thetool is rotated 90°. The tool is held at angle to the path of the wheelto construct grooves in the master tool that become more shallow as themachining stroke progresses from the tip to the shank of the master toolblank. The die is formed using the master tool by hobbing or pressingthe master tool into die stock. This may take several strokes to obtainthe fully formed die. The die is then used to cold form a punch which isin turn used as the tool to cold form a recess in the head of thefastener.

Drivers are constructed in a manner similar to the punches and areidentical in shape to the punch and master tool.

The manufacture of the PHILLIPS cross head master is relatively straightforward because the driving surfaces are symmetrical. This is not thecase with respect to the manufacture of the vertical driving surfaces ofthe modified cross head fastener of the '994 patent. In this instance,it has been found that to obtain an accurate relationship with respectto the driving surfaces of a wing of the recess and that of the driver,it is necessary to construct the forward driving face vertical and thereverse driving face at a small taper. The planes of these taperedsurfaces, if extended, would intersect at an included angle of 2.5° orlooking at it another way the reverse driving surface is tapered at anangle of 2.5° to the forward driving surface. This provides the neededrelief from cam out in the forward direction where it is moreproblematic.

To accomplish this according to the above process, the master tool blankis machined using eight strokes, between which, the blank is rotated andthe angle of the blank with respect to the wheel path is also adjusted.This involves the machining of compound angles, i.e., angles which aredependent on other angles and is extremely complex and difficult tocontrol to the required tolerances. The machining of the master toolsfor such asymmetrical cross head screws is an acknowledged challenge.

Although attempts have been made to combine the Robertson square drivewith a PHILLIPS type drive, see U.S. Pat. Nos. 5,358,368 and 5,020,954,these have not been well received and do not accommodate the use of anasymmetrical driver. U.S. Pat. No. 2,082,748 discloses a fastener thatcombines a Robertson recess with a PHILLIPS type recess and a slot typerecess. It appears that such attempts have generally compromised theadvantage of one type of recess or the other.

It is a purpose of this invention to provide a recess for a fastenerwhich will accommodate a square driver, and symmetrical and asymmetricalcross bladed type drivers. This recess therefore, will accommodate thewide variety of fastener drivers currently in use. It is a purpose ofthis invention to provide such a recess while avoiding the complexmanufacturing requirements of the asymmetrical type cross head andwithout compromising the beneficial features of the common driverconfigurations. It is also a purpose to provide a unique driver to takeand advantage of all of the unique features of the new recess.

SUMMARY OF THE INVENTION

A cross type recess is constructed on the head of a threaded fastenerhaving its driving faces tapered symmetrically. The taper is designed toprovide an included angle between the driving surfaces equal to thestandard included angle of an asymmetrical cross head recess. A squaredrive recess is incorporated into the geometry of the cross type recessat the outer portion of the recess, thereby forming an overall recessconfiguration that will accommodate the standard drivers associated withthe square drive recess, the symmetrical cross head drivers, and theasymmetrical cross head drivers. In addition such fasteners can be usedwhich is constructed with the full geometric form of the recess. Thisallows fasteners, formed with the recess of this invention, to be drivenwith the majority of drivers prevalent in the current market.

The cross head recess of this invention is formed from a punch which isin turn formed from a die which is in turn formed by a machined mastertool. The master tool is machined with a grinding wheel using fourpasses to obtain symmetrically shaped grooves defined by drivingsurfaces tapered at ½ of the included angle of the standard asymmetricalcross type recess.

The cross portion of the recess extends to the full depth of the recesswhile the square portion of the recess extends to a lesser depth. Thedepth of the square portion of the recess is chosen to be within thegeometry of the cross recess, thereby providing a clearance for theridges at the corners between opposite wing faces of the asymmetricaltool. Such ridges are a by product of the manufacturing process ofasymmetrical type drivers and are one factor which hinders theinterchangeable use of the cross type drivers. Another hindering factoris the symmetrical versus asymmetrical tapering of the driving surfaces.By using a symmetrical taper as in the original cross head design, at anangle which accommodates the included angle of the asymmetrical crosshead design, it has been found that each type of driver can be used inthe recess of this invention without compromising the torque transmittalcharacteristics of the drivers. In addition “cam out” is minimized andthe manufacturing process is simplified.

In order to accommodate the multiple drivers the recess of thisinvention has a unique shape. Engagement with anyone of the standarddrivers will provide an effective transmission of torque from the driverto the fastener utilizing the unique features of each type of driver.Nevertheless a driver especially constructed to match the recess willhave further advantages over any of the individual types. Such a driveris constructed to match the master tool or punch of this invention forapplication specifically for engagement with the universal recess ofthis invention.

DESCRIPTION OF THE DRAWING

The invention is described in more detail below with reference to theattached drawing in which:

FIG. 1 is a perspective view of a master tool used in the formation of arecess in accordance with this invention;

FIG. 2(a) is a perspective view of a tip of an asymmetrical driver;

FIG. 2(b) is a perspective view of a tip of a symmetrical driver;

FIG. 3 is an a top view of a fastener showing the recess according tothis invention; and

FIG. 4 is a cut away perspective view of the head of a fastener showingthe recess according to this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The specifications for recesses and drivers of the types referencedabove and further described herein are controlled by industrialstandards to provide continuity of configuration across the wide varietyof applications and manufacturers. Therefore when a particular fasteneris described herein, a fastener complying with such standards areintended. The Industrial Fastener Institute (IFI) promulgates suchstandards in particular in ASME rev. B18.6.5M, 1998. In these standardsType I refers to symmetrical cross recessed fasteners, Type Ia refers toasymmetrical cross recessed fasteners, and Type III refers to squarerecessed fasteners.

As shown in FIGS. 3 and 4, the recess 30 of this invention is formedwith wing shaped cross slots 1-4. These slots are defined by opposingwalls 5-12 which provide the driving surfaces of the fastener 13. Therecess 30 has an opening at the top surface 14 of fastener head 15 andextends downward, a depth d₁, to its bottom 16. At the top surface 15,the opening of the recess 30 has a combination square and cross shapedopening. Square driving surfaces 17-20 are formed to an intermediatedepth d₂ which is less than the full depth d₁ of the recess 30.

The opposing walls 5 and 12 form the slot 1 and are constructed at anangle to the vertical, i.e. to the longitudinal axis x shown in FIG. 4,in which the walls are converging from top to bottom. The angle ofconvergence A is also referred to as the included angle and is equal tothe included angle of the asymmetrical cross head fastener as set out inthe applicable ASME standard. This angle is obtained by tapering thewalls 5-12 symmetrically at angles B and C, as shown in FIGS. 1 and 4.According to the standard, this would mean that angles B and C are1.25°, thereby forming a converging angle A of 2.5°. The opposing walls6 and 7, 8 and 9, and 10 and 11 are similarly constructed to provide across head recess 30 with symmetrical slots having opposing drivingsurfaces converging at 2.5°.

The outer portion of the recess 30 is shaped to accommodate a squaredriver according to the applicable standard. Substantially verticalwalls 17-20 intersect at right angles as shown in phantom in FIG. 3.Walls 17-20 include transition shoulders 21-24 which taper downward toform the bottom seat of the square drive portion of the recess 30 offastener 15. The depth d₂ of the square drive portion is selected toposition the square drive driving surfaces, i.e. walls 17-20, within thegeometry of the cross drive portion of recess 30. This will provide aclearance for the asymmetrical driver 80, as described below.

To manufacture the recess 30, a master punch 40 is constructed of toolgrade steel, as shown in FIG. 1. The purpose of the master punch 40 isto form a die (not shown) having a female die cavity in the form of therecess 30. The die is used to form punches for cold forming the recess30 into the heads of fasteners and to form drivers optimally configuredto engage the recess 30. Master punch 40 is machined having grooves 41which are defined by symmetrically tapered walls 42-49. The walls 42-49also define blades 50-53 which converge towards tool axis y, from shankto tip. The blades 50-53 match the cross shape of the recess 30 andextend the full length l₁ of the active surface of master punch 40.Adjacent walls, such as 42 and 43 of blade 50, converge at an includedangle A with each wall forming an angle to the vertical, B and C of ½ ofincluded angle A. For the purpose of this description vertical refers toa plane parallel to axis y.

To form the square drive portion of recess 30, the master punch 40 ismachined with intermediate shoulders 54-57, 54 and 55 being shown inFIG. 1 (56 and 57 not shown), shoulders 54-57 taper towards axis y. Theshoulders extend to axially parallel walls 60-63 having a length l₂ (62and 63 not shown). These shoulders and walls match the shape of thesquare drive portion of recess 30.

In operation the square driver fits into the square portion of therecess 30 in a normal fashion for effective transmission of torque tothe screw. A tip of a standard PHILLIPS style cross driver 100 is shownin FIG. 2(b). The driver 100 is constructed with blades 101-104 definedby driving surfaces 105-112. The driving surfaces converge symmetricallytowards its tip at included angles of between 8°-27°. The driver 100will also fit easily into the recess 30, but its driving surfaces willengage primarily at the top of the recess. This is an advantage as thisprovides an increased leverage for the transmission of torque.

A tip of an asymmetrical driver 80, which includes those for use withfasteners sold under the trademark POZIDRIV, is shown in FIG. 2(a). Thedriver 80 is constructed with blades 81-84 defined by driving surfaces85-92. The driving surfaces converge asymmetrically towards its tip atincluded angles of 2.5°. Driver 80 includes ridges 93-96 at the cornersbetween opposite driving surfaces 85-92 of the asymmetrical tool. Theridges 93-96 are a by-product of the manufacturing process ofasymmetrical type drivers and are one factor which hinders theinterchangeable use of the cross type drivers. Because of the clearanceformed by the depth of the square head portion of the recess 30, anasymmetrical driver, such as driver 80, also fits snuggly into therecess 30 with a slight clearance at its non-driving side, but aneffective engagement over the face of the driving surface. Because ofthe small angle of taper, i.e. 1.25°, “cam out” is minimized with thesymmetrical driver. Fastener heads which employ the recess of thisinvention, therefore, accommodate all of the prevailing drivers in amanner that maintains the advantages of each without compromisingperformance.

Although it is intended that the fasteners utilizing the recess 30 willbe used with the existing drivers constructed in accordance withindustry standards, it is understood that it would be useful to have anew driver formed to fully engage the unique configuration of thesurfaces of recess 30. A driver of this type is constructed having theshape of the master tool 40 while incorporating standard clearancetolerances to facilitate insertion and release of the new driver intoand from the recess 30. All of the surfaces of a new driver constructedto optimize the use of the recess of this invention are shown in FIG. 1and further description is unnecessary.

1. A tool for forming a recess, said tool having a working portionextending from a shank to a tip a first distance, said working portionof said tool comprising: a cross winged portion extending said firstdistance from said shank to said tip having an overall cross wing outerprofile, said wings being formed by adjacent walls, wherein saidadjacent walls converge, from said shank to said tip, at a symmetricallyformed included angle having an overall size that is substantiallyequivalent to an included angle of an asymmetrical cross recessedfastener manufactured in conformity with a standard for type Iafasteners; and a square portion, having an overall square outer profile,extending a second distance, that is less than said first distance,wherein said overall square outer profile is within said overall crosswing outer profile.
 2. A tool for forming a recess, according to claim1, wherein said included angle is 2.5 degrees.
 3. A tool for forming arecess, according to claim 1, wherein said adjacent walls are eachinclined at an angle of 1.25 degrees to the vertical to cause saidconvergence.
 4. A tool for forming a recess, according to claim 1,wherein the tool is used to form a recess in the head of a fastener. 5.A tool for forming a recess, according to claim 1, wherein the tool isused to form a cavity in a die.